Optical head, disk apparatus, method for manufacturing optical head, and optical element

ABSTRACT

An optical head which implements high recording density of a recording medium and which is miniaturized in size and improved in data transfer rate, a disk apparatus, and a method for manufacturing the optical head are provided. A laser beam is emitted from a semiconductor laser, the laser beam is collimated by the collimator lens to a collimated beam and reflected by a mirror, condensed by an condense lens, and incident to an incident surface of a transparent condensing medium. The condensed beam which was incident to the incident surface is refracted by the incident surface, the refracted beam is condensed on a condense surface, a beam spot is formed on the condense surface, and a near field wave leaks from a small aperture. The near field wave leaked from the small aperture propagates in a recording layer of a recording. The beam is served for recording/reproduction on the recording layer.

This is a continuation of application Ser. No. 09/271,868 filed Mar. 18,1999 now U.S. Pat. No. 6,154,326. The entire disclosure of the priorapplication(s) is hereby incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical head and disk apparatus which usenear field wave, and a method for manufacturing optical heads, and moreparticularly, relates to an optical head which implements high densityrecording on a recording medium and a small-sized optical head ofimproved data transfer rate, a disk apparatus, a method formanufacturing optical heads, and an optical element for an optical head.

2. Description of Related Art

In the field of optical disk apparatus, the optical disk has changedhistorically from the compact disk (CD) to the digital video disk (DVD),which has a large recording capacity and is capable of high densityrecording. The recent development of high performance computers and highresolution displays has resulted in increasing demand for large capacityrecording.

The recording density of an optical disk depends basically on thediameter of an optical spot formed on a recording medium. Recently, thenear field wave technology in the field of the microscope has beenapplied to the optical recording technology as a technology forminiaturizing the beam spot diameter. As the conventional optical diskapparatus which uses the near field wave, for example, the optical diskdescribed in the literature (Jpn. J. Appl. Phys., Vol. 35 (1996) P. 443)and U.S. Pat. No. 5,497,359 has been known.

FIG. 21(a) and FIG. 21(b) show an optical disk apparatus described inthe literature (Jpn. J. Appl. Phys., Vol. 35 (1996) P. 443). As shown inFIG. 21(a), the optical disk apparatus 190 is provided with asemiconductor laser 191 that emits a laser beam 191 a, a coupling lens192 that changes the laser beam 191 a emitted from the semiconductorlaser 191 to a collimated beam 191 b, and an optical fiber 193 which ispolished in a taper shape having a larger diameter at the incident end193 a and a smaller diameter at the emission end 193 b, and providedwith a probe 194 that introduces the collimated beam 191 b which comesfrom the coupling lens 192 from the incident end 193 a, and a recordingmedium 195 on which the information is recorded by means of the nearfield wave 191 c that leaks from the emission end 193 b of the opticalfiber 193.

The recording medium 195 has a recording layer 195 a consisting ofGeSbTe, which is a phase change recording medium, which recording mediumis heated by incident near field wave 191 c, and then the heating causesphase change between crystal/amorphous, and difference in reflectancebetween both phases is utilized for recording.

The optical fiber 193 has the incident end 193 a having a diameter of 10μm and the emission end 193 b having a diameter of 50 nm, and is coatedwith a metal film 194 b consisting of a metal such as aluminum withinterposition of a clad 194 a to prevent the beam from leaking tosomewhere other than the emission end 193 b. The diameter of the nearfield wave 191 c has the approximately same diameter as the diameter ofthe emission end 193 b, therefore the high density recording of several10 Gbits/inch² is possible.

For reproduction, as shown in FIG. 21(b), a near field wave 191 c havingsuch a low power as it does not cause phase change is irradiated ontothe recording layer 195 a by use of the same optical head as used forrecording, the reflected beam 191 d from the recording layer 195 a iscondensed on a photomultiplier 197 by means of a condenser lens.

FIG. 22 shows an optical head of an optical disk apparatus disclosed inU.S. Pat. No. 5,497,359. The optical head 50 is provided with ancondense lens 52 that condenses a collimated beam 51 and an Super SIL(Super Solid Immersion Lens) 54 having the form of bottom-cut sphereplaced with the bottom plane 54 a perpendicular to the condensed beam 53from the condense lens 52. The collimated beam 51 is condensed by thecondense lens 52 and the condensed beam 53 is incident onto thespherical incident surface 54 b, the condensed beam 53 is refracted atthe incident surface 54 b and condensed on the bottom surface 54 a toform a beam spot 55 on the bottom surface 54 a. Because the wavelengthof the beam becomes short in inversely proportional to the refractiveindex in the internal of the super SIL 54, the diameter of the beam spotbecomes small in proportion to it. A part of the beam condensed on thebeam spot 55 is totally reflected toward the incident surface 54 b, butthe beam leaks partially from the beam spot 55 to the outside of thesuper SIL 54 as a near field wave 57. A recording medium having theapproximately same refractive index as that of the super SIL 54 islocated at the close distance from the bottom surface 54 a so that thedistance is sufficiently smaller than a wavelength of the wave, then thenear field wave 57 is coupled with the recording medium 56 andpropagates in the recording medium 56. The information is recorded onthe recording medium 56 by the propagation beam.

By structuring the Super SIL 54 so that the collimated beam 51 iscondensed at the position r/n (r denotes the radius of the Super SIL)distant from the center 54 c of the semi-spherical surface 54 b, thespherical aberration due to the Super SIL 54 is reduced and thenumerical aperture in the Super SIL 54 is increased, and further thediameter of the beam spot 55 is minimized. In detail, the beam spot 55is minimized according to the equation 1.

D _(½) =kλ/(n·NAi)=kλ/(n ² ·NAo)  (1)

where,

D_(½): beam spot diameter where the intensity becomes a half of themaximum intensity.

k: proportional constant (normally around 0.5) which depends on theintensity distribution of an optical beam

λ: wavelength of an optical beam

n: refractive index of an Super SIL 54

NAi: numerical aperture in an Super SIL 54

NAo: numerical aperture of an incident beam to an Super SIL 54

The collimated beam 51 is condensed as the beam spot 55 withoutabsorption on the optical path and high optical utilization factor isobtained. As the result, a beam source having a relatively low output issufficient for use and the reflected beam is detected without aphotomultiplier.

PROBLEM OF THE RELATED ART

However, according to the conventional optical disk apparatus 190,though a beam spot having a size of several ten nm is formed on arecording medium, a laser beam which enters an optical fiber 193 ispartially absorbed in its inside due to the taper shape of the opticalfiber 193, and the optical utilization factor is as low as 1/1000 orlower disadvantageously. Because of the low optical utilization factor,a photomultiplier 197 is undesirably required to detect the reflectedbeam 191 d and the photomultiplier leads to a large sized as well asexpensive optical head. Further, slow response speed of thephotomultiplier 197 and heavy weight optical head result in theslowed-down tracking speed. Due to many problems such as a low transferrate due to slow rotation of an optical disk, much improvement isrequired for practical use.

FIG. 23 is a graph for describing the problem of the conventionaloptical head 50 shown in FIG. 22, which was presented by T. Suzuki in#OC-1 in Asia-Pacific Data Storage Conference (Taiwan, 1997. 7), therelation between the refractive index n of a SIL 54 and NAo is shown.There is a reversal relation between NA of incident beam to the SIL 54,namely the maximum value θmax of the incident angle θ, and therefractive index n of the SIL 54, and the two values cannot be increasedindependently. It is understandable as shown in the graph that thepossible maximum value NAomax of NAo of the incident beam becomesgradually smaller with increasing of the refractive index of the SIL 54,because the beam having a large incident angle which is caused fromincreased NAo larger than the maximum NAomax enters directly into therecording medium 56 without passing through the SIL 54 and the size ofthe beam spot 55 positioned at the recording medium 56 becomes largerinstead. For example, if n=2, then NAomax is 0.44, the product n·NAomaxdoes not exceeds the value of 0.8 to 0.9 for any combination of n andNAomax. This value is the theoretical limit and the actual value issmaller (0.7 to 0.8) than the theoretical value.

B. D. Terris et al. presented their test result on the Super SIL inAppl. Phys. Lett., Vol. 68, (1996), P. 141. According to the testreport, a laser beam having a wavelength of 0.83 μm was condensed toform a beam spot having a diameter of 0.317 μm by use of a Super SILhaving a refractive index n=1.83 placed between an condense lens and arecording medium, that is, D_(½)=λ/2.3 was obtained. In this case, NA is0.4, n·NAmax is about 0.73. The experimental result with use of thissystem suggests the possibility of high recording density as high as0.38 Gbits/cm², which is several times that of the conventional system.

In detail, the conventional optical head 50 with a laser beam having awavelength of 400 nm gives a beam spot having a diameter of 0.2 μm atthe best because there is a reversal relation between the refractiveindex of the SIL and the maximum Naomax, and the theoretical limit ofthe product n·NAomax is 0.8 to 0.9, and the actual limit is 0.7 to 0.8though the optical utilization factor is high. The diameter of the beamspot is several times larger than that of conventional example in whicha probe 194 is used for condensing, and thus the conventional opticalhead 50 is disadvantageous in that the recording density cannot beenhanced.

FIG. 24 shows a conventional optical head described in the literature“NIKKEI ELECTRONICS (Jul. 15, 1998) (No.718)”. The optical head is,called as SIM (Solid Immersion Mirror) type, provided with a transparentcondensing medium 101 having a concave incident surface 101 a on which acollimated laser beam 2 b is incident, a condense plane 101 b providedon the position facing to the incident surface 101 a, a planerreflecting surface 101 c provided on the periphery of the condense plane101 b, and a non-spherical reflecting surface 101 d formed on theperiphery of the incident surface 101 a, a planer reflecting film 102formed on the surface of a planer reflecting surface 101 c, and anon-spherical reflecting film 103 formed on the surface of thenon-spherical reflecting surface 101 d. A collimated laser beam 2 bcomes to the incident surface 101 a of the transparent condensing medium101 of the optical head having the structure as described herein above,the incident collimated laser beam 2 b which comes to the incidentsurface 101 a is diffused on the incident surface 101 a, the diffusedbeam 2 d is reflected on the planer reflecting film 102, the reflectedbeam 2 e is reflected on the non-spherical reflecting film 103, thereflected beam is condensed on the condense plane 101 b, and a beam spot9 is formed on the condense plane 101 b. The near field wave 10 whichleaks from the condense plane 101 b is served for recording and readingon the recording layer 8 a of a recording medium 8. The numeral apertureNA of the planer reflecting surface 101 c of the transparent condensingmedium 101 is around 0.8, and the refractive index of the transparentcondensing medium 101 is 1.83, and NA in the transparent condensingmedium 101 is approximately 1.5.

The conventional optical head shown in FIG. 24 gives a beam spot havinga diameter of as large as 0.35 to 0.39 μm and is disadvantageous in thatthe recording density cannot be enhanced because of the minimizing limitof the spot diameter formed on a condense plane of the transparentcondensing medium.

Accordingly, it is the object of the present invention to provide anoptical head and optical disk apparatus which are capable of highdensity recording on a recording medium and enhancing the sizeminimization and data transfer rate, and a method for manufacturing theoptical head.

To achieve the above-mentioned object, the present invention provides anoptical head, comprising: a laser emitting a laser beam; an opticalsystem including a transparent condensing medium which has a condensesurface and condensing the laser beam to form a beam spot on thecondense surface; and a shade provided on the transparent condensingmedium and having an aperture, wherein the aperture is positioned atwhich the beam spot is formed and a size of the aperture is smaller thana size of the beam spot.

SUMMARY OF THE INVENTION

To achieve the above-mentioned object, the present invention provides Anoptical head, comprising: a laser emitting a laser beam; an opticalsystem including a transparent condensing medium which has a condensesurface and condensing the laser beam to form a beam spot on thecondense surface; and a shade provided on the transparent condensingmedium and having an aperture, wherein the aperture is positioned atwhich the beam spot is formed and an area of the aperture is smallerthan a size of the beam spot.

To achieve the above-mentioned object, the present invention provides adisk apparatus, comprising: a rotator which rotates a disk which holdsan information, an optical head recited above; and an optical headactuator coupled with the optical head.

To achieve the above-mentioned object, the present invention provides amethod for manufacturing an optical head comprising: a step in which atransparent condensing medium having a condense plane on which anincident laser beam forms a beam spot is prepared; a step in which aphoto-resist having a outside diameter smaller than that of the beamspot is formed on the transparent condensing medium; a step in which aconcave is formed by removing the area where the photo-resist does notcover on the transparent condensing medium by etching to thepredetermined depth smaller than the wavelength of the laser beam, and astep in which a shade film having an aperture with a smaller area thanthe size of the beam spot is formed by depositing a shading material onthe concave.

To achieve the above-mentioned object, the present invention provides amethod for manufacturing an optical head recited above, comprising astep for forming the shade with the aperture on the transparentcondensing medium, wherein the shade forming step includes a etchingprocess performed from the condense surface side of the transparentcondensing medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for illustrating the main part of an optical head inaccordance with the first embodiment of the present invention.

FIG. 2(a) is a diagram for illustrating a transparent condensing mediumand a shading film in accordance with the first embodiment.

FIG. 2(b) is a bottom view of the diagram shown in FIG. 2(a).

FIG. 3(a) to FIG. 3(d) are diagrams for describing a method for formingthe shading film in accordance with the first embodiment.

FIG. 4(a) and FIG. 4(b) are diagrams for illustrating modified examplesof the shading film in accordance with the first embodiment.

FIG. 5 is a diagram for illustrating the main part of an optical head inaccordance with the second embodiment of the present invention.

FIG. 6(a) is a diagram for illustrating the main part of an optical headin accordance with the third embodiment of the present invention.

FIG. 6(b) is a bottom view of the diagram shown in FIG. 6(a).

FIG. 7 is a diagram for illustrating the main part of an optical head inaccordance with the fourth embodiment of the present invention.

FIG. 8(a) is a diagram for illustrating the main part of an optical headin accordance with the fifth embodiment of the present invention.

FIG. 8(b) is a diagram for illustrating a shading film of the opticalhead shown in FIG. 8(a).

FIG. 9(a) is a diagram for illustrating an optical disk apparatus inaccordance with the first embodiment of the present invention.

FIG. 9(b) is a cross sectional view along the line A—A in FIG. 9(a).

FIG. 10 is a diagram for illustrating in detail the optical disk inaccordance with the first embodiment of the present invention.

FIG. 11 is a diagram for illustrating the optical head in accordancewith the first embodiment.

FIG. 12(a) to FIG. 12(c) are diagrams for illustrating the main part ofthe optical head of an optical disk apparatus in accordance with thesecond embodiment of the present invention.

FIG. 13 is a diagram for illustrating an optical disk apparatus inaccordance with the third embodiment of the present invention.

FIG. 14 is a diagram for illustrating an optical disk apparatus inaccordance with the fourth embodiment of the present invention.

FIG. 15 is a diagram for illustrating the main part of an optical diskapparatus in accordance with the fifth embodiment of the presentinvention.

FIG. 16 is a diagram for illustrating a semiconductor laser inaccordance with the fifth embodiment.

FIG. 17 is a diagram for illustrating a shading film in accordance withthe fifth embodiment.

FIG. 18 is a diagram for illustrating the main part of the optical headof an optical disk apparatus in accordance with the sixth embodiment ofthe present invention.

FIG. 19 is a graph for describing the relationship between the detectedoptical power and reproduction rate.

FIG. 20(a) is a vertical cross sectional view of the optical head of anoptical disk apparatus in accordance with the seventh embodiment of thepresent invention.

FIG. 20(b) is a horizontal cross sectional view or the optical headshown in FIG. 20(a).

FIG. 21(a) is a diagram for illustrating a conventional optical diskapparatus.

FIG. 21(b) is a diagram for illustrating the reproduction operation ofthe conventional optical disk apparatus shown in FIG. 21(a).

FIG. 22 is a diagram for illustrating an optical head of anotherconventional optical disk apparatus.

FIG. 23 is a graph for describing the relationship between therefractive index n and NA.

FIG. 24 is a diagram for illustrating a conventional optical head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a main part of an optical head 1 in accordance with thefirst embodiment of the present invention. The optical head 1 isprovided with a semiconductor laser 2 for emitting a laser beam 2 a, acollimator lens 3 for converting the laser beam 2 a from thesemiconductor 2 to a collimated beam 2 b, a mirror 4 for reflecting thecollimated beam 2 b from the collimator lens 3 to the verticaldirection, an condense lens 5 for condensing the collimated beam 2 breflected on the mirror 4, a transparent condensing medium 6 on which abeam spot 9 on a condense surface 6 b from the incident beam 2 ccondensed by the condense lens 5 is incident, and a shading film 7having a small aperture 7 a formed by deposition on the surface of thecondense surface 6 b of the transparent condensing medium 6.

A red laser (630 nm), which is the shortest commercially availablewavelength, or an AlGaInN-based blue laser, which starts to be supplied,may be used as the semiconductor laser 2. By use of a blue laser (400 nmor 410 nm), the beam spot diameter can be minimized to 0.15 μm orsmaller.

FIG. 2(a) shows the transparent condensing medium 6 and the shading film7, and FIG. 2(b) is the bottom view thereof.

The transparent condensing medium 6 can be formed from dense flint glass(refractive index=1.91), or crystalline material such as cadmium sulfideCdS (refractive index=2.5), or zincblende ZnS (refractive index=2.37),and the refractive index of the material has no limitation as long as amaterial has a refractive index of 1 or higher, a material having afurther higher refractive index may be used. Dense flint glass having arefractive index of 1.91 is used in the embodiment of the presentinvention. The use of crystalline material leads to the minimization ofa beam spot diameter by 20% in comparison with dense flint glass. Asshown in FIG. 2(a), the transparent condensing medium 6 has a cut-bottomspherical shape (Super SIL structure) so that the condensed beam 2 c,which is incident on the spherical incident surface 6 a, from thecondense lens 5 is refracted on the incident surface 6 a and therefracted beam 2 d is condensed on the condense surface 6 b on thebottom to form a beam spot 9. Here, to form a beam spot 9 on thecondense surface 6 b means the condense surface 6 b is positioned withinthe depth of focus of the beam spot 9.

The shading film 7 having a thickness smaller than a laser wavelength(for example 10 nm) consists of titanium (Ti) which is a shadingmaterial, on which a small aperture 7 a having a diameter (for example,50 nm) smaller than the diameter of a beam spot 9 and smaller than thewavelength of a laser beam at the position corresponding to the beamspot 9, and which prevents the beam from directly emission of the beamspot 9 to the outside and forms a near field wave 10 having theapproximately same diameter as that of the small aperture 7 a. The smallaperture 7 a is circular in the present embodiment but may be othershape such as rectangle. The use of a rectangular aperture leads to thesmaller track pitch and the higher recording density in comparison withthe circular aperture. The diameter of the small aperture 7 a will besmaller than 50 nm in the future with further development in highrecording density technology and small aperture forming technology inthe optical disk technology field.

To condense the beam to the position r/n (r and n are radius andrefractive index of the transparent condensing medium 6 respectively)distant from the center 6 c of the sphere, the spot diameter of a beamspot 9 is represented by the following equation (1) as described in thedescription of the conventional example.

D _(½) =kλ/n·NAi)=kλ/n ² ·NAo)  (1)

wherein

NAi denotes the numerical aperture in the transparent condensing medium6 and,

NAo denotes the numerical aperture of an incident beam to thetransparent condensing medium 6.

As shown in the equation (1), the diameter of a beam spot 9 is minimizedin inverse proportion to the refractive index n of the transparentcondensing medium 6, and the minimized diameter minimizes the sphericalaberration in condensing. However, because the possible incident angle θof the condensed beam 2 c, namely the numerical aperture NAo and therefractive index n are associated each other in the reversalrelationship, the two cannot be large independently. The product of therefractive index n and the maximum NA value is about 0.88, but actuallythe product is about 0.8 due to the eclipse of a beam. Accordingly, theminimum beam spot diameter D_(½) min is represented by the followingequation (2).

D _(½)min=kλ/(0.8n)−0.6λ/n(when k=0.5)  (2)

The use of dense flint glass (refractive index=1.91), which has thelargest refractive index among amorphous materials, for the transparentcondensing medium 6 and the use of a red laser (wavelength of 630 nm) asthe semiconductor laser 2 gives the minimum beam spot diameter D_(½) minof 0.20 μm. The use of a blue laser (400 nm) gives the minimum beam spotdiameter D_(½) min of about 0.13 μm. These beam spots 9 have theapproximately Gaussian intensity distribution.

The small aperture 7 a prevents the propagation beam from emission fromthe small aperture 7 a because the diameter of the small aperture 7 ais, for example, as small as {fraction (1/10)} of the laser wavelength,and a near field wave 10 leaks across the same distance as the diameterof the small aperture 7 a. When a dielectric material, such as arecording medium 8, is placed near the recording medium 8 to expose itto the near field wave 10, the near field wave 10 enters and propagatesinto the recording layer 8 a of the recording medium 8, and the wavefunctions for recording/reading on the recording layer 8 a. The lightintensity of the propagation beam is approximated by the followingequation (3).

[Expression 1] $\begin{matrix}{I = {{I_{0} \times {\int^{a}{\int^{a}{^{{- {({x^{2} + y^{2}})}}/\omega^{2}}\quad {{x}\quad \cdot \quad {y}}}}}} = {I_{0} \times \frac{\pi}{2} \times {\int^{a}{r\quad ^{({{- r^{2}}/\omega^{2}})}\quad {r}}}}}} & (3)\end{matrix}$

wherein Io: full power of a laser

ω: radius of a beam spot 9 at the condense surface 6 b

a: radius of the small aperture 7 a

In detail, in the case of a red laser, the beam intensity of a laserbeam which passes through the small aperture 7 a is about 15% of thefull power of the beam spot 9, and in the case of blue laser, the beamintensity is more than 20%, thus the condensing efficiency is improvedby 100 times that of the case in which a conventional optical fiber isused.

FIG. 3(a) to FIG. 3(d) show an embodiment related to a method of thisinvention for deposit-forming of the shading film 7 and forming of thesmall aperture 7 a. First, a photoresist film 70 for electron beamexposure is coated on the bottom surface 6 d of the bottom-cut shapedtransparent condensing medium 6, and exposed (FIG. 3(a)) to an electronbeam so that a portion 70 a which corresponds to the small aperture 7 aand a protective portion 70 b which corresponds to the periphery of theshading film 7 remain, and after development, the bottom surface 6 d isetched about 100 A anisotropically by means of dry etching to form theprojection 6 f and the bottom surface 6 g (FIG. 3(b)). CF₄-base gas isused as the etching gas. Next, the Ti film 71 having a thickness ofabout 100 A for shading is deposited on the entire surface by means ofspattering (FIG. 3(c)), the photoresist film 70 (70 a and 70 b) isdissolved to lift off the Ti film 71 on the portion 70 a for the smallaperture 7 a and the protective portion 70 b for the shading film 7(FIG. 3(d)). The shading film 7 having the small aperture 7 a is formedas described hereinabove. Other films which has the light shadingproperty and the adhesiveness to a glass can be used for the shadingfilm 7 besides Ti film.

When the projection 6 f of the transparent condensing medium 6 fillsinside the small aperture 7 a, as shown in this embodiment, comparing tothe embodiment that the projection 6 f is not formed and the smallaperture 7 a is filled with air, the air gap between the top of theprojection 6 f and the surface of the optical disk decreases and thenthe propagation efficiency of the near field wave is improved. Here, thetop of the projection 6 f may project or caved from the surface of theshading film 7. Further, as shown in FIG. 3, the top of the projection 6f positioned inside the aperture 7 and the surface of the shading film 7can be flat viewing from the near field wave emission side of thetransparent condensing medium 6, then the divergence of the near fieldwave can be reduced and the higher recording density can be attained.

In case that the projection 6 f is formed to the transparent condensingmedium 6, like this embodiment, the top surface of the projection iscorresponded to the condense surface 6 b. Therefore to form a beam spoton a condense surface 6 b means the top surface of the projection ispositioned within the depth of focus of the beam spot. However if thethickness of the shading film 7 is as thin as the height of theprojection 6 f, like this embodiment, the top surface of the projection6 f and the bottom surface 6 g where the shading film is formed are bothpositioned with in the depth of the focus of the beam spot mostly, theadjustment of the beam spot forming position is not much affected by theformation of the projection 6 f.

Further more, during the formation process of the small aperture 7 withthe well-known etching process, when the etching process is applied fromthe condense surface 6 b of the transparent condensing medium 6, thesidewall of etched-portion, such as the projection 6 f, is exposed tothe etching gas and etched gradually, then the portion is properlyformed incline. When the shading film is formed around the etchedportion, the small aperture 7 a of the shading film 7 is tapered alongthe optical path of the near field wave, which is effective to improvethe condensing efficiency.

Next, the operation of the optical head 1 in accordance with theabove-mentioned first embodiment is described. A laser beam 2 a emittedfrom the semiconductor laser 2 is converted to a collimated beam 2 b bythe collimator lens 3 and reflected by the mirror 4, and then condensedby the condense lens 5 and comes onto the incident surface 6 a of thetransparent condensing medium 6. The condensed beam 2 c which hasentered through the incident surface 6 a is refracted on the incidentsurface 6 a, the refracted beam 2 d is condensed on the condense surface6 b to form a beam spot 9 on the condense surface 6 b, and the nearfield wave 10 leaks from the small aperture 7 a. The near field wave 10which has leaked from the small aperture 7 a enters and propagates intothe recording layer 8 a of the recording medium 8, and the beamfunctions for recording/reproduction on the recording layer 8 a.

According to the optical head 1 in accordance with the above-mentionedfirst embodiment, the near field wave which has leaked from the beamspot 9 formed on the condense surface 6 b is diaphragmed by the smallaperture 7 a, therefore the near field wave spot formed on the recordingmedium 8.

The diaphragming of the near field wave by use of the small aperture 7 ahaving a diameter smaller than the wavelength of the laser beam 2 a doesnot much reduce the central optical intensity of the near field wavefrom the small aperture 7 a to bring about high optical efficiencyfactor. Therefore, a semiconductor laser 2 having a relatively lowoutput such as several mW can be used as a beam source. Because thereflected beam from the recording medium 8 increases in proportion tothe propagation beam from the small aperture 7 a, an Si photo-detector,which is generally used for optical disk memory, can be used fordetection of the reproduction beam without using a photomultiplier, thusthe optical head 1 can be lightweight and high speed readable.

FIG. 4(a) and FIG. 4(b) show modified examples of the shading film 7.The shading film 7 may have the concave or projected conical surface asshown in FIG. 4(a), which is formed by inclining the surface of thebottom plane 6 g to incline the surface to be etched with respect to theincident beam during etching process of the bottom plane 6 d of thetransparent condensing medium 6. Alternatively as shown in FIG. 4(b),the shading film 7 may have a rough surface, which is formed by use ofhigh speed etching technique with supplying a relatively large currentduring etching of the bottom plane 6 d of the transparent condensingmedium 6. The high reflectance on the surface 7 b of the shading film 7results in high beam intensity of the beam reflected on the shading film7 in comparison with a signal beam to be returned from the smallaperture 7 a and results in the reduced amplification factor of thefront end amplification during signal processing to a lower S/N. On theother hand, the high absorptance on the shading film 7 results in thetemperature rising of the portion of the shading film 7 where the beamspot 9 is irradiated to adversely influence recording unpreferably. Toavoid such problems, the structures as shown in FIG. 4(a) and FIG. 4(b)are used, and in such a structure, the reflected beam 2 e does notreturn to the condense lens 5, and S/N is improved. On the other hand,the reflected beam which passes the small aperture 7 a passes throughthe same path as the incident beams 2 c and 2 d and enters a beamdetector (omitted in the drawing). As described hereinabove, theproportion of the stray beam which enters the beam detector is reducedto result in the increased amplification factor of the DC typepreamplifier and improved S/N.

FIG. 5 shows the main part of the optical head in accordance with thesecond embodiment of the present invention. The optical head 1 has asemi-spherical transparent condensing medium 6 (SIL type), and othercomponents are same as those shown in the first embodiment. Thecondensed beam 2 c which has come onto the incident surface 6 a of thetransparent condensing medium 6 is condensed at the center of thesphere. In this case, the condensed beam 2 c is not refracted on theincident surface 6 a, the numerical aperture NA in the transparentcondensing medium 6 is therefore the same as NA at the position wherethe beam has come out from the condense lens 5, and the increased NA dueto refraction cannot be attained. Accordingly, the beam spot isrepresented by the following equation (4) in this case.

D _(½) =kλ/n·NAo)  (4)

wherein NAo represents the numerical aperture of the incident beam tothe SIL type transparent condensing medium 6.

According to the optical head 1 in accordance with the above-mentionedsecond embodiment as similar to the first embodiment, because thediameter of the near field wave 10 is determined by the diameter of thesmall aperture 7 a and does not depend on the diameter of the beam spot9, and is therefore not so influenced by the aberration and positional,NAo can be about 0.8, which is evaluated as relatively large as 0.8 incomparison with the optical head which uses a conventional SIL, and thecondensing equivalent to that brought about by the Super SIL structuredescribed in the first embodiment can be obtained. In detail, a redlaser (wavelength of 630 nm) and a blue laser (400 nm) give the minimumbeam spot diameters of 0.2 μm and 0.13 μm respectively, and the lightintensity of the near field wave which leaks from the small aperture 7a, namely the optical utilization efficiency, is same as that obtainedin the first embodiment.

FIG. 6(a) shows the main part of an optical head in accordance with thethird embodiment of the present invention, and the FIG. 6(b) shows thebottom view thereof. The optical head 1 is provided with a semiconductorlaser 2 for emitting a laser beam 2 a, a collimator lens 3 forconverting the laser beam 2 a from the semiconductor laser 2 to acollimated beam 2 b, a transparent condensing medium 6 for condensingthe collimated beam 2 b from the collimator lens 3 and forming a beamspot 9 on the condense surface 6 b, a reflecting film 11 which isdeposited and formed on the surface of a reflecting surface 6 e of thetransparent condensing medium 6, and a shading film 7 having a smallaperture 7 a which is deposited and formed on the surface of a condensesurface 6 b of the transparent condensing medium 6.

The transparent condensing medium 6 consists of, for example, denseflint glass (refractive index=1.91), and has an incident surface 6 afrom which the collimated beam 2 b enters, a reflecting surface 6 e forreflecting the collimated beam 2 b which comes onto the incident surface6 a, and a condense surface 6 b on which a beam spot 9 is formed.

The reflecting surface 6 e is a part of a paraboloid of revolution. Theprincipal axis of the cross section (6 e) of the paraboloid ofrevolution is assigned to x-axis and the vertical axis is assigned toy-axis, and the focus position is assigned to (p, 0), then the crosssection (6 e) is represented by the following equation (5).

y ²=4px  (5)

The condensing in the internal of the transparent condensing medium 6with use of the paraboloid of revolution principally brings aboutnon-aberration condensing (Optics, by Hiroshi Kubota, Iwanami Shoten, p.283), and a beam is condensed on a beam spot 9 by one condense mirror.In this method, no restriction on the refractive index of thetransparent condensing medium 6 and the numerical aperture NA of acondensed beam by a reflecting surface 6 e is applied, and a highrefractive index can give NA value near 1 even though the refractiveindex is high. Therefore, the beam spot diameter is represented by thefollowing equation (6) in this case.

D _(½)=λ/(n·NAr)  (6)

wherein NAr denotes the numerical aperture of the reflected beam fromthe reflecting surface 6 e.

Assuming the focus position of the paraboloid of revolution P=0.125 mmand the top end of the paraboloid of revolution (x, y)=(2 mm, 1 mm),then the convergent angle from the top end of 60 degrees or larger isobtained, and gives NA of the reflecting surface 6 e of 0.98, this valueis 1.6 or more times larger than NA=0.6 in the conventional DVD.

According to the optical head 1 in accordance with the above-mentionedthird embodiment, though NAr is normally limited to about 0.9 withdesign margin actually for a red laser (wavelength of 630 nm) and bluelaser (400 nm), the beam spot diameter can be minimized to 0.19 μm and0.12 μm for a red laser (wavelength of 630 nm) and blue laser (400 nm)respectively, the beam quantity of a near field wave 10 which leaks fromthe small aperture 7 a, namely the optical utilization factor, can beincreased by about 20% in comparison with the first embodiment.

No chromatic aberration occurs because of reflection type condensing.

The focus position deviation due to temperature change is reducedbecause the optical system of the present embodiment is a so-calledinfinite system, in which the laser beam 2 b between the collimator lens3 and the incident surface 6 a of the transparent condensing medium 6 iscollimated.

FIG. 7 shows the main part of an optical head in accordance with thefourth embodiment of the present invention. The optical head 1 isprovided with a transparent condensing medium 6 having a planerreflecting surface 6 e and a reflecting hologram which is served as areflecting film 11 on the surface of the reflecting surface 6 e, andother components are same as those used in the third embodiment. Thereflecting hologram may be a binary hologram or a volume hologramconsisting of organic photosensitive material. A reflecting filmcomprising a highly reflecting metal layer consisting of a metal such asaluminum may be provided on the outside of the hologram. The planershape of the reflecting surface 6 e of the transparent condensing medium6 helps improve the productivity in comparison with the thirdembodiment.

FIG. 8(a) and FIG. 8(b) show the main part of an optical head inaccordance with the fifth embodiment of the present invention. As shownin FIG. 8(a), an optical head 1 uses a transparent condensing medium 6of SIM (Solid Immersion Mirror) type, and provided with a semiconductorlaser 2 for emitting a laser beam 2 a, a collimator lens 3 forconverting the laser beam 2 a from the semiconductor laser 2 to acollimated beam 2 b, a mirror 4 for reflecting the collimated beam 2 bfrom the collimator lens 3 in the vertical direction, an incidentsurface 6 a with a form of concave on which the collimated beam 2 benters from the mirror 4, a condense surface 6 b disposed at theposition facing the incident surface 6 e, a reflecting film 11 depositedand formed on the reflecting surface 6 e of the transparent condensingmedium 6, and a shading film 7 having a small aperture 7 a deposited andformed on the condense surface 6 b of the transparent condensing medium6. The small aperture 7 a is formed at the position corresponding to abeam spot 9 as shown in FIG. 8(b) in the same manner as in the firstembodiment.

Next, the operation of the optical head 1 in accordance with the fifthembodiment is described. The laser beam 2 a from the semiconductor 2 iscollimated by the collimator lens 3, reflected by the mirror 4, andincident upon the incident surface 6 a of the transparent condensingmedium 6. The collimated beam 2 b which was incident upon the incidentsurface 6 a is diffused on the incident surface 6 a, the diffused beam 2d is reflected on the shading film 7, the reflected beam 2 e isreflected by the reflecting film 11 and condensed on the condensesurface 6 b to form a beam spot 9 on the condense surface 6 b, and anear field wave 10 leaks from the small aperture 7 a. The near fieldwave 10 which has leaked from the small aperture 7 a is incident intothe recording layer 8 a of the recording medium 8, and the beam isserved for recording/reading on the recording layer 8 a.

According to the optical head 1 in accordance with the above-mentionedfifth embodiment, the recording density in the track direction X isincreased as in the first embodiment, and further the condense lens usedin the first embodiment is unnecessary, the structure can be simplified.Because the position of the focus point does not change even if thetransparent condensing medium 6 expands or shrinks, the optical head 1is usable under temperature changing conditions without auto focusingservo control. The shading film 7 and the condense surface 6 b may havea structure shown in FIG. 4(a) and FIG. 4(b).

Further, because the diameter of the small aperture 7 a is less thanabout 0.2 μm, for example, to form the beam spot at the small aperture 7a having minute aperture precisely, the erroneous of the positioningbetween the aperture and the beam spot is needed to be at least lessthan 0.1 μm. Like as shown in the first and second embodiment which usethe SIL and condense lens, because the converged beam condensed by thecondense lens is incident on the SIL, the fluctuation of the relativeposition between the incident laser beam, the condense lens and SILcauses the fluctuation of the position where the beam spot is formed. Onthe other hand, because the optical head described in the third andfifth embodiment which do not use condense lens, by the collimated beamis incident directly to the transparent condensing medium, thefluctuation between the collimated beam and the medium 6 is notinfluenced to the position where the beam spot is formed. This isadvantageous because the less precision in the production is required.

FIG. 9(a) shows an optical disk apparatus in accordance with the firstembodiment of the present invention, FIG. 9(b) is a cross sectional viewalong the line A—A in FIG. 9(a). The optical disk apparatus 100 isprovided with an optical disk 12 comprising a disk-like plastic plate120 having a recording layer 121 consisting of GeSbTe phase changematerial formed on one surface which is rotated by a motor not shown inthe drawing with interposition of the rotation shaft 30, an optical head1 for optical recording and optical reproduction on the recording layer121 of the optical disk 12, a linear motor 32 for moving the opticalhead 1 in the tracking direction 31, a suspension for supporting theoptical head 1 from the side of the linear motor 32 an optical headdriving system 34 for driving the optical head 1, and a signalprocessing system 35 for processing signals obtained from the opticalhead 1 and for controlling the optical head driving system 34.

The linear motor 32 is provided with a pair of fixed members 32 adisposed along the tracking direction 31 and a movable coil 32 b whichmoves on the pair of fixed members 32 a. The optical head 1 is supportedby the movable coil 32 b with interposition of the above-mentionedsuspension 33.

FIG. 10 shows the detail of the optical disk 12. The optical disk 12 isa high recording density optical disk corresponding to minimization of anear field wave 10 formed by the optical head 1. The plastic plate 120comprises, for example, a polycarbonate substrate having grooves 12 aformed on one side. The optical disk 12 has a recording layer 121 formedby laminating an Al reflecting film layer (thickness of 100 nm) 121 a,an SiO₂ layer (thickness of 100 nm) 121 b, a GeSbTe recording layer(thickness of 15 nm) 121 c, and an SiN layer (thickness of 50 nm). Inthe present embodiment, the information is recorded on lands 12 b, thetrack pitch is 0.07 μm, and the depth of a groove 12 a is about 0.06 μm.The mark length is 0.05 μm, the recording density is 130 Gbits/inch²,which corresponds to a 12-cm disk having the recording capacity of 210GB, this recording capacity is 45 times larger than that of aconventional DVD. Various recording media such as ROM disks having pits,recording/reproduction media which use magneto-optic recording materialsand phase change materials, and write once media on which recording isperformed by forming pits by beam absorption in colorant may be used.

FIG. 11(a) and FIG. 11(b) show the optical head 1 in accordance with the6th embodiment of the present invention, FIG. 11(a) is a side view andFIG. 11(b) is a bottom view. The optical head 1 has a flying slider 36which flies on the optical disk 12, and provided on the flying slider 36are a single edge emitting semiconductor laser 2 consisting of, forexample, AlGaInP for emitting a laser beam 2 a having a wavelength of630 nm, a collimator lens 3 that collimates the laser beam 2 a emittedfrom the semiconductor laser 2 into a collimated beam 2 b, a seat plate37A comprising a molten quartz plate mounted on the flying slider 36, aholder 37B comprising a molten quartz plate for fixing the semiconductorlaser 2 and collimator lens 3 on the seat plate 37A, a polarized beamsplitter 13 for separating the beam into the collimated beam 2 b fromthe semiconductor laser 2 and the reflected beam from the optical disk12, a quarter wavelength plate 38 for converting the linearly polarizedcollimated beam 2 b from the semiconductor laser 2 to a circularlypolarized beam, a mirror 4 for reflecting the collimated beam 2 b in thevertical direction, an condense lens 5 and a upper transparentcondensing medium 6′ for condensing the collimated beam 2 b reflected bythe mirror 4, and an optical detector 15 mounted on the seat plate 37Ato which the reflected beam from the optical disk 12 comes through thebeam splitter 13. All components are contained in a head case 39, andthe head case 39 is fixed on the end of the suspension 33.

The upper transparent condensing medium 6′ consists of, for example,dense flint glass having a refractive index n=1.91, has a diameter of 1mm, and has a height of about 1.3 mm. The upper transparent condensingmedium 6′ has the Super SIL structure which is the same as thetransparent condensing medium 6 shown in FIG. 1, the flying slider 36consists of a transparent medium having the same refractive index asthat of the transparent condensing medium 6, the bottom surface 36 a ofthe flying slider 36 corresponds to the condense surface 6 a, and a beamspot 9 is formed on the bottom surface 36 a of the flying slider 36.Therefore one transparent condensing medium 6 is composed of the uppertransparent condensing medium 6′ and the flying slider 36. A shadingfilm 7 having a small aperture 7 a is deposited and formed on the bottomsurface 36 a of the flying slider 36 in the same manner as shown in FIG.1.

The flying slider 36 has a groove 36 b so that a negative pressure iscaused on the area other than the peripheral area of the optical spot 9formed on the bottom surface 36 a as shown in FIG. 11(b). The negativepressure caused by the groove 36 b and the spring force of thesuspension 33 function to keep the space between the flying slider 36and the optical disk 12 fixedly, which space is the flying height. Theflying height is about 0.06 μm in the present embodiment. The bottomsurface 36 c is served as a sliding surface. Further, the flying heightis very small and at the same time the gap between the top of theprojection and the optical disk must be determined precisely. As shownin FIG. 11(a), by forming the top of the projection of the transparentcondensing medium 6 and the bottom surface of the flying slider 36 onthe same plane, the gap between the projection and the optical disk canbe controlled precisely only by adjusting the flying height of theflying slider 36 without colliding to the optical disk and damaged.

The optical head driving system 34 causes phase change betweencrystalline state and amorphous state in the recording layer 121 bymodulation of the output beam from the semiconductor laser 2correspondingly to recording signals during recording operation, andsignals are recorded as the difference in the reflectance duringrecording, on the other hand, during reproducing operation, the laserbeam 2 is irradiated continuously without modulation of the output beam,and the difference in the above-mentioned reflectance on the recordinglayer 121 is detected by the optical detector 15 as the variation of thereflected beam intensity.

The signal processing system 35 generates an error signal for trackingand data signal based on the reflected beam from the optical disk 12detected by the optical detector 15, generates a high frequency errorsignal and a low frequency error signal through a high-pass filter and alow-pass filter respectively from the error signal, and then trackingcontrol is performed on the optical head driving system 34 based onthese error signals. The tracking error signal is generated according toSample Servo System (Optical Disk Technology, Radio Technology Co., P.95), in which wobbled tracks are marked on tracks intermittently and theerror signal is generated based on the reflection intensity change.Because the recording signal and tracking error signal are separatedtime-divisionally in the case of Sample Servo System, both signals areseparated by a gate circuit in a reproducing circuit. The SCOOP method,which uses a photo-sensor with a non-separated photoreceptor for thebeam detection, can be well combined with the sample servo system. Theerror signal may be generated by push-pull system that utilizesinterference with the reflected beam from the groove 12 a.

Next, the operation of the optical disk apparatus in accordance with theabove-mentioned 6th embodiment is described. The optical disk 12 isrotated at a predetermined rotation speed by a motor not shown in thedrawing, and the flying slider 36 flies on the optical disk 12 by theaction of the negative pressure generated from rotation of the opticaldisk 12 and the spring force of the suspension 33. A laser beam 2 aemitted from the semiconductor 2 driven by the optical head drivingsystem 35 is collimated to a collimated beam 2 b by the collimator lens3, passes through the polarized beam splitter 13 and the quarterwavelength plate 35, and comes to the incident surface 6 a of the uppertransparent condensing medium 6′. The collimated beam 2 b is convertedfrom a linearly polarized beam to a circularly polarized beam by thequarter wavelength plate 38 when passing through the quarter wavelengthplate 38. The circularly polarized collimated beam 2 b is condensed bythe condense lens 5, refracted on the incident surface 6′ a of the uppertransparent condensing medium 6′ and condensed, and condensed on thebottom surface 36 a of the flying slider 36. A small beam spot 9 isformed on the bottom surface 36 a of the flying slider 36. The partialbeam of the beam spot 9 leaks from the small aperture 7 a under the beamspot 9 to the outside of the bottom surface 36 a of the flying slider 36as a near field wave 10, and the near field wave 10 propagates in therecording layer 121 of the optical disk 12 and optical recording oroptical reproduction is performed. A reflected beam reflected on theoptical disk 12 traces the path of the incident beam reversely,refracted on the incident surface 6′a of the upper transparentcondensing medium 6′ and reflected by the mirror 4, converted to alinear polarized beam having the polarization plane which is 90 degreesdifferent from the incident beam (2 a) by the quarter wavelength plate38, reflected in the direction of an angle of 90 degrees by thepolarized beam splitter 13, and enters the optical detector 15. Thesignal processing system 35 generates an error signal for trackingcontrol and data signal based on the reflected beam from the opticaldisk 12 which was incident to the optical detector 15, and performstracking control on the optical head driving system 34 based on theerror signal. Because recording/reproduction is performed withoutautomatic focusing control, an automatic focusing control mechanism isunnecessary, and the weight of the optical head 1 is significantlyreduced and the size is miniaturized. The optical head 1 has a length ofabout 8 mm, width of about 4 mm, and height of about 6 mm, and theweight of the optical head 1 is about 0.6 g, the total weight of themovable part including the weight of the movable coil 32 b of the linearmotor 32 is about 2.0 g, and the frequency band of tracking is 50 kHz orhigher, and the gain is 60 or higher. The decentering of the disk thatis minimized to a value as small as 25 μm allows tracking whichsatisfies the required accuracy of 5 nm under 600 rpm rotation speedcondition. In this case, the ravage transfer rate is 60 Mbps, whichallows UGA level video signals to be recorded or reproduced.

According to the optical disk apparatus 100 in accordance with theabove-mentioned 6th embodiment, the maximum angle of refraction on theincident surface 6′a of the upper transparent condensing medium 6′ is 60degrees, NA of 0.86 is obtained, as the result, a small beam spot havinga spot diameter D_(½) of about 0.2 μm is obtained, and about 20% of thebeam spot can be incident on the recording layer 121 of the optical disk12 as a near field wave 10 through the small aperture 7 a having adiameter of 50 nm, and thus the super high density (180 Gbits/inch²)recording/reproduction is realized.

Because by employing Sample Servo System the recording signal and thetracking error signal are separated time-divisionally, a divided-typeoptical detector 15 is not required, and, for example, a PIN photodiodehaving a size of 1 mm can be used sufficiently. The optical detector 15is not necessarily of divided-type, and a detection system is allowed tobe simplified and lightweight.

Sample Servo System is used to generate tracking control error signal inthe above-mentioned embodiment, however, the wobbled track system, inwhich the recording track is waved periodically and modulation of thereflected beam intensity due to waving is detected synchronously withthe waving frequency to generate an error signal, may be used.

The three-spot system may be used instead as it is used in tracking of aROM CD. In detail, a diffraction grating is inserted between thecollimator lens 3 and the polarized beam splitter 13, optical detectionelements for detecting the ± first order reflected beam from the diskare provided on both sides of the main beam detection element, and theerror signal is generated based on the difference between outputs.

Push-pull type control, in which unbalance between right and leftdiffracted beams from the side of the recording track is detected togenerate an error signal, may be used. In this case, the diffractedbeams are detected by a two-divided type optical detection element, anda differential output error signal is generated.

Further, the optical head 1 in the present embodiment may be used as itis for recording and reproduction on a write once type disk (a disk onwhich pits are formed by beam absorption of colorant).

Further, the optical head 1 can be used for magneto-optic recording byuse of a magneto-optic medium in a manner, in which a thin film coil isprovided on the periphery of the beam spot 9 formed on the bottomsurface 36 a of the flying slider 36 and magnetic field modulation isperformed. However, it is necessary to replace the polarized beamsplitter 13 with a non-polarized beam splitter and to provide ananalyzer before the optical detection element because the rotation ofthe polarization plane of the beam is detected by a polarizationanalysis to generate the signal for reproduction.

The edge emitting type laser is used as the laser source in the presentembodiment, however, a Vertical Cavity Surface Emitting Laser (VCSEL)may be used. In the case of a surface emitting type laser, though themaximum output in the base mode (TEM00) is as low as about 2 mW, whichis {fraction (1/10)} or smaller than that of the end surface emittingtype laser, because in the present embodiment the beam spot diameter ismuch smaller than that for the conventional optical apparatus and thebeam density is ten or more times higher, the surface emitting typesemiconductor laser can be used for recording. In the surface emittingtype semiconductor laser the wavelength variation due to temperature issmall, and the chromatic aberration correction can be omitted.

FIG. 12 shows the main part of an optical disk apparatus in accordancewith the 7th embodiment. FIG. 12(a) is a partial plan view of atransparent condensing medium 6, FIG. 12(b) is a front view of the same,and FIG. 12(c) is a view of the driver for the transparent condensingmedium 6. An optical head 1 of the optical disk apparatus has a installopening 36 d 6 on a flying slider 36, for installing the transparentcondensing medium and a pair of piezoelectric elements 41 and 41 isprovided on the flying slider 36 with holders 42 for scanning thetransparent condensing medium 6 in the tracking direction 40. Othercomponents are the same as those used in the optical disk apparatus 100in accordance with the 6th embodiment. The transparent condensing medium6 has a condense surface 6 b, and the condense surface 6 b is disposedso as to be in the almost same plane as the bottom surface 36 b of theflying slider 36. The condense surface 6 b of the transparent condensingmedium 6 may be projected or recessed from the neighboring shading film.

As shown in FIG. 12(c) respectively, each element of the pair ofpiezoelectric elements 41 and 41 comprises a plurality of electrodefilms 411 connected to the electrode terminals 410 and 410 andmulti-layered PZT thin films (thickness of about 20 μm) 412 formedbetween electrode films 411. The piezoelectric element 41 is depositedand formed on the holder 42, the pair of piezoelectric elements 41 and41 support the transparent condensing medium 6 and functions to scan inthe direction perpendicular to the beam namely in the tracking direction40. The deformation direction may be set along the beam direction to setthe gap between the condense surface 6 b and the optical disk.

According to the above-mentioned optical disk apparatus in accordancewith the 7th embodiment, for example, the weight of the transparentcondensing medium 6 is as light as 5 mg or lighter, the resonancefrequency of the system which supports the transparent condensing medium6 can be 300 kHz or higher, and the deformation of 0.5 μm or larger isobtained with an applied voltage of 5 V between electrode terminals 410and 410.

Further, two-step control by use of the piezoelectric element and linearmotor 32 enable to obtain a band of 300 kHz at the gain of 80 dB, andthe optical disk is tracked with 5 nm accuracy under high rotation speedof 3600 rpm. In the present embodiment, the transfer rate is increasedto a rate six times that of the optical disk apparatus 100 in the firstembodiment, namely 360 Mbps.

The use of a multi-beam optical head which will be described hereinaftergives a rate eight times higher, and a transfer rate of nearly 3 Gbps isobtained. The average seek speed of 10 ms or faster is achieved for a 12cm disk. The access time for 3600 rpm rotation is reduced to a value asshort as 20 ms or shorter.

FIG. 13 shows an optical disk in accordance with the 8th embodiment ofthe present invention. Though the linear motor is used for seekoperation in the 6th embodiment, however, a rotation type linear motor43, which is used for a hard disk, is used in the 8th embodiment. Theoptical head 1 is connected to the rotation type linear motor 43 withinterposition of a suspension 33 supported rotatably around a rotatableshaft 33 a. The structure described hereinabove allows the rotation typelinear motor 43 to be disposed on the outside of the optical disk 12,and the optical head 1 can be made thin and the whole structure of theoptical disk apparatus 100 can be miniaturized. Further, the opticaldisk 12 can be rotated at high speed (3600 rpm), and the average datatransfer rate of 360 Mbps or faster is implemented.

FIG. 14 shows an optical disk apparatus in accordance with the 9thembodiment of the present invention. In this optical disk apparatus 100,an optical head 1 having the transparent condensing medium 6 is appliedto the disk stack type optical disk apparatus having five optical disks,the optical disk apparatus 100 is provided with five optical disks 12,each optical disk has two recording layers 121 and 121 on the top andbottom surface of a plastic substrate 120, 10 optical heads 1 which flyover the recording layers 121 of respective optical disks 12,suspensions 33 which support respective optical heads 1 rotatably withinterposition of a rotation axis 44, and a rotation type linear motor 45for driving the suspensions 33. The recording layer 121 may be a phasechange type medium or a magneto-optic medium. The rotation type linermotor 45 comprises a movable member 45 a connected to the suspensions 33and electromagnets 45 c and 45 c combined with interposition of a yoke45 b for driving the movable member 45 a. The structure of this opticalhead 1 is basically the same as that shown in FIG. 6, the transparentcondensing medium 6 having a paraboloid of revolution and AlGaInN-basedlaser (630 nm) are used, and the beam spot diameter is 0.2 μm. The diskdiameter is 12 cm, and the track pitch and mark length are 0.07 μm and0.05 μm respectively, the capacity per one surface is 300 GB.

According to the optical disk apparatus 100 in accordance with theabove-mentioned 9th embodiment, the information is recorded on fiveoptical disks 12, and the capacity as large as 3 TB is implemented.

The optical head 1 shown in FIG. 6 or FIG. 7 may be used. Thereby theheight of an optical head can be 3 mm or lower, the height of an opticaldisk apparatus can be lowered and the capacity per volume is increased.

FIG. 15 shows the main part of an optical disk apparatus in accordancewith the 10th embodiment of the present invention. The optical diskapparatus 100 is provided with a plurality of independently drivablelaser elements (for example, eight), and provided with a semiconductorlaser 2 in which a plurality of laser beams 2 a are emitted from aplurality of respective laser elements, a collimator lens 3 forcollimating the laser beams 2 a from the semiconductor laser 2 toincident beams 2 b′, a mirror 4 for reflecting the incident beams 2 b′in the predetermined direction, an condense lens 5 for condensing theincident beams 2 b′ reflected by the mirror 4, a transparent condensingmedium 6 to which the condensed beams 2 c′ condensed by the condenselens 5 are incident and in which a plurality of beam spots 9 are formedon the condense surface 6 b, which has the same structure as shown inFIG. 1, a shading film 7 having a plurality of small apertures 7 aformed by deposition on the surface of the condense surface 6 b of thetransparent condensing medium 6, an optical disk 12 having a recordinglayer 121 consisting of GeSbTe phase changing material on one side of adisk-shaped plastic plate 120 which is rotated by a motor not shown inthe drawing, a polarized beam splitter 13 for separating the beamreflected on the optical disk 12 from incident beams 2 b′, andeight-divided optical detector 15 to which laser beams 2 e separated bythe beam splitter 13 are incident through a condenser lens 14.

FIG. 16 shows the semiconductor laser 2. The semiconductor laser 2 is anedge emitting semiconductor, and has active layers 20 a, p-typeelectrodes 20 b, and n-type electrode 20 c. The interval d_(l) of thep-type electrodes 20 b is prescribed to be, for example, 15 μm, and theinterval of the laser beams 2 a is set to be 15 μm resultantly.

FIG. 17 shows the shading film 7. The shading film 7 has eight smallapertures 7 a correspondingly to the number of laser beams 2 a. Becausethe NA of the collimator lens 3 is 0.16, NA of the transparentcondensing medium 6 is 0.8, and the interval d₁ of the laser beams 2 ais 15 μm, the interval of the beam spots 9 on the condense surface 6 bnamely the interval d₂ of the small apertures 7 a is 3 μm. The arrayaxis direction 7 b of the small apertures 7 a is slightly deviated fromthe track of the optical disk 12 so that the respective small apertures7 a are positioned just above adjacent tracks. In detail, the intervalof the respective adjacent small apertures 7 a in the perpendiculardirection to the recording tracks is arranged so as to be equal to thetrack pitch (in this case, 0.07 μm). The inclination angle between thearray axis direction 7 b of the small apertures 7 a and the tracks(omitted) is 23 milliradian, the inclination is adjusted by controllingthe inclination of the support for the laser array and by controllingphotolithography during forming for the small aperture array.

Next, the operation of the optical disk apparatus 100 in accordance withthe above-mentioned 10th embodiment is described. A plurality of laserbeams are emitted from the semiconductor laser 2, the plurality of laserbeams 2 a from the semiconductor laser 2 are collimated by thecollimator lens 3 to form a prescribed incident beams 2 b′, the incidentbeams 2 b′ pass through the polarized beam splitter 13 and reflected bythe mirror 4, and condensed by the condense lens 5, refracted on theincident surface 6 a of the transparent condensing medium 6 andconverted on the condense surface 6 b. A plurality of beam spots 9 areformed on the condense surface 6 b. A plurality of near field waves 10leak from the plurality of respective small apertures 7 a under theplurality of respective beam spots 9, and the near field waves 10propagate in the recording layer 121 of the optical disk 12 and areserved for optical recording or optical reproduction. The reflectedbeams reflected on the optical disk 12 return reversely on the path ofthe incident beams, are refracted on the incident surface 6 a of thetransparent condensing medium 6 and reflected by the mirror 4, separatedfrom the incident beams 2 b′ by the polarized beam splitter 13, andcondensed into the eight-divided optical detector 15 by the convertinglens 14.

According to the optical disk apparatus 100 in accordance with theabove-mentioned 10th embodiment, the eight near field waves 10 which canbe modulated independently of each other from the respective eight smallapertures 7 a are served independently for recording/reproductionsimultaneously on respective eight recording tracks, therecording/reproduction transfer rate is increased eight times. Becausethe array length of the small apertures is about 20 μm and the bend ofthe track corresponding to the array length is as small as 0.007 μm,which is {fraction (1/10)} of the track width, the track deviation dueto the track bend is negligible. The number of small apertures is notlimited to eight, may be increased or decreased depending on the use.The transparent condensing medium 6, such as shown in FIG. 4, FIG. 5,FIG. 6, or FIG. 7 may be used.

Further, exposing the plural apertures with one beam spot and using thenear field waves leaked from these apertures, the frequency range of thetracking can be reduced. Furthermore, the edge emitting typesemiconductor laser generates plural emission points along the activelayer 20 a of the semiconductor laser, as shown in FIG. 16, because therow of the beams depend on the direction of the semiconductor laserelement, in other words, depending on the direction of the active layer,the direction can be selected arbitrary. Also in a single beam type ofthe edge emission semiconductor laser, because the beam becomes ovalshape along the active layer, then the direction of the active layer canbe selected properly, either.

FIG. 18 shows an optical disk apparatus in accordance with the 11thembodiment of the present invention. An optical head 1 of the opticaldisk apparatus is different from the optical head 1 shown in FIG. 1 inthe outside diameter of the shading film 7, and other structures are thesame as those shown in FIG. 1. The periphery of the shading film 7 has adiameter slightly larger than that of the condensed beam 2 c, whichcorresponds to the diameter of the condensed beam spot on the condensesurface. The optical disk 12 is provided with a protective film 12 h, arecording layer 12 i, an interference layer 12 j, and reflecting layer12 k. In the present embodiment, the total thickness of the protectivefilm 12 h, recording layer 12 i, interference layer 12 j, and reflectinglayer 12 k is about 100 nm, and the distance between the protective film12 h and the small aperture 7 a is about 50 nm.

Next, the operation of the optical head 1 in accordance with theabove-mentioned sixth embodiment is described. The condensed beam 2 cfrom the condense lens is refracted on the spherical incident surface 6a of the transparent condensing medium 6, and the refracted beam 2 d iscondensed on the condense surface 6 b. A beam spot 9 is formed on thecondense surface 6 b. The near field wave 10 which leaks from the smallaperture 7 a of the shading film 7 enters and propagates in the opticaldisk 12, and is reflected by the reflecting layer 12 k of the opticaldisk 12. The reflected beam 2 k reflected by the reflecting layer 12 kpasses not only the small aperture 7 a of the shading film 7 but alsothe outside of the shading film 7 to enter the optical detector throughthe transparent condensing medium 6 and the condense lens.

The intensity distribution of a near field wave 10 from a small aperture7 a is approximated to the intensity distribution 1 in the case that thesmall aperture 7 a is assumed to be a perfect diffusing surface in therecording medium. In this case, the broadening of the beam is maximized,and the angular distribution is represented by Cos θ. The beam isreflected by the reflecting film 12 k in the direction of thetransparent condensing medium 6 with the distribution unchanged.Assuming that the viewing angle of the contour of the small aperture 7 aand shading film 7 are θ₁ and θ₂ respectively, then the proportionI_(r1)/I₀ of the beam which returns to the small aperture 7 a and theproportion I_(r2)/I₀ of the beam which returns to the peripheral areaare represented respectively by the following equations (7) and (8),where the transmittance of the small aperture 7 a is denoted by Tn, andthe medium reflectance is denoted by Rb.

[Expression 2]

I _(r1) /I ₀ =Tn×Rb×∫ ^(2π)∫₀ ^(θ) ^(₁) Cos θdθ·dφ=2π×Tn×Rb×[Sin θ] ₀^(θ) ^(₁)   (7)

[Expression 3]

I _(r2) /I ₀ =Tn×Rb×∫ ^(2π)∫_(θ2) ^(π/4) Cos θdθ·dφ=2π×Tn×Rb×[Sinθ]_(θ2) ^(π/4)  (8)

The small aperture 7 having a diameter of 50 nm gives Tn of 0.15 and Rbof about 0.2 for the phase change medium, therefore the outside diameterof the shading film of 0.2 μm gives I_(r1)/I₀ of 0.0025 and I_(r2)/I₀ of0.02. As the result, it is possible to improve the intensity about tentimes by introducing the beam of the peripheral area of the shading film7. The smaller the diameter of the small aperture 7 a is, the moreeffective. Because the beam of the peripheral area is refracted on theincident surface 6 a of the transparent condensing medium 6 and entersthe internal and the beam which has returned from the small aperture 7 adiffuses around the small aperture 7 a, the directivities of both beamsare slightly different from each other, however the diameter of thetransparent condensing medium 6 of about 1 mm is sufficiently largerthan the film thickness (150 nm) of the small aperture 7 a and recordingmedium, thus the difference is negligible, it is possible to introduceboth beams together into the optical detector, and the reflected beamintensity is increased.

FIG. 19 shows the relationship between the detected optical power whichis required for maintaining the code error rate of 1×10⁻⁹ and thereproduction rate. In FIG. 19, the solid line represents a duty ratio of0.1 and the broken line represents a duty ratio of 1, and the line groupA represents the quantum efficiency of the optical detector of 0.1 andthe line group B represents the quantum efficiency of the opticaldetector of 1. The detected optical power in the present embodiment isabout −30 bBm, so the reproduction rate can be 10⁹ bit/sec or higher.(G. Ohtsu, Electronics, the issue of May 1996, p.92)

FIG. 20 shows an optical head of an optical disk apparatus in accordancewith the 12th embodiment of the present invention. FIG. 20(a) is avertical cross sectional view and FIG. 20(b) is a horizontal crosssectional view. In the present embodiment, the optical head 1 shown inFIG. 8 is applied to the optical disk apparatus 100 shown in FIG. 9. Theoptical head 1 has a flying slider 36 which flies on the optical disk12, and provided on the flying slider 36 are an end surface emittingtype semiconductor laser 2 consisting of, for example, AlGaInP foremitting a laser beam having a wavelength of 630 nm, a collimator lens 3for collimating the laser beam 2 a emitted from the semiconductor laser2 into a collimated beam 2 b, a holder 37A comprising a molten quartzplate mounted on the flying slider 36, a holder 37B comprising a moltenquartz plate for fixing the semiconductor laser 2 and collimator lens 3on the holder 37A, a holder 37C for holding the semiconductor laser 2with interposition of a piezoelectric element 41, a polarized beamsplitter 13 for separating the beam into the collimated beam 2 b fromthe semiconductor laser 2 and the reflected beam from the optical disk12, a quarter wavelength plate 38 for converting the linearly polarizedcollimated beam 2 b from the semiconductor 2 to a circularly polarizedbeam, a mirror 4 for reflecting the collimated beam 2 b in the verticaldirection, a transparent condensing medium 6 for condensing thecollimated beam 2 b reflected by the mirror 4 shown in FIG. 8, areflecting layer 11 deposited on the reflecting surface 6 e of thetransparent condensing medium 6, and an optical detector 15 fixed to theseat plate 37A for receiving the reflected beam from the optical disk 12through the beam splitter 13. All components are contained in a headcase 39, and the head case 39 is fixed to the end of the suspension 33.A shading film 7 having a small aperture 7 a is formed by deposition onthe bottom surface 36 a of the flying slider 36 in the same manner asshown FIG. 8.

According to the optical disk apparatus 100 in accordance with the 12thembodiment, a near field wave which leaks from the beam spot 9 formed onthe bottom surface 36 a of the flying slider 36 to the outside passesthrough the small aperture 7 a, thereby enabling super-high densityoptical recording/reproduction as described in the explanation of theoptical disk apparatus 100 of the first embodiment and miniaturizationof the optical head 1 in the height direction. The optical head 1 may beapplied to the optical disk apparatus 100 such as shown in FIG. 13, FIG.14, and FIG. 15.

Further, the optical head can be composed as so-called separate type,which the heavy parts, such as laser and photo-detector, is provided ona stationary portion and on the movable portion the parts which has tobe set on the movable portion, such as transparent condensing medium andslider, are installed. However, as described before, the optical head ofthis invention need a precise positioning of the aperture and the beamspot on the condense surface with the degree of less than 0.1 μm. Theseparate type may be difficult enough to adjust the stationary portionand the movable portion with such accuracy, because the up and downmotion of the surface of the optical disk, the vibration of the movableportion or the deformation of installed parts by the thermal alterationtherefore at least the laser and the transparent condensing medium ispreferred to be installed on a same body such as moving together. Thenthe difference of the position between the beam spot and the aperturecaused by these fluctuation or the deformation can be improved.

The method to detect the information recorded on the disk can be appliednot only the method to detect the reflecting beam from the optical diskas shown in the embodiments, but also the method to detect theinformation magnetically such as the well-known GMR (Gigantic MagneticResistive) sensor, of course.

In the embodiments above, the optical element, such as a collimator, areflector, a condense lens and a transparent condensing medium, consistsof one part, but the optical element can be composed of plural parts, atleast while the condition that the beam spot is condensed on the surfaceof the transparent condensing medium and the aperture is positioned atthe beam spot is satisfied.

Further, when the spot is formed on the transparent condensing medium bya reflector, the gap between the reflector and the transparentcondensing medium may be allowable, but to prevent the sphericalaberration the reflector and the transparent condensing medium areadhered to each other without the air gap. The reflector may be a castmade from, for example, the metal, but the film is preferable to improvethe adherence to the medium.

The shade is not limited to the film, such as described in theembodiments. The minimum requirement is the film enable the near fieldwave to leak from its aperture. Therefore the shade can be an adhesivethin sheet or the periphery of the aperture on the transparentcondensing medium which is chemically treated as to shade the beamsubstantially. Because of the thinness of the shade and the precisenessof the formation of the aperture the shade film is preferred.

According to the present invention, as described hereinbefore, a nearfield wave which leaks from a beam spot formed on a condense surface tothe outside of a transparent condensing medium is diaphragmed by a smallaperture, thereby enabling minimization of the near field wave spotformed on a recording medium. As the result, high recording density of arecording medium is implemented.

Because condensing the beam on the condense surface of the transparentcondensing medium and obtaining the near field wave from the aperturelocated at where the beam is condensed, the high optical utilizationefficiency factor is obtained. The high optical utilization factorallows use of a small-sized lightweight beam source and an opticaldetector, thereby enabling miniaturization of the optical head andoptical disk apparatus, and improvement of the data transfer rate.

What is claimed is:
 1. An optical head, comprising: a laser emitting alaser beam; a transparent condensing medium having a condense surface onwhich a condensed laser beam forms a beam spot; and a shade provided onthe transparent condensing medium and having an aperture, wherein theaperture is positioned at which the beam spot is formed and an area ofthe aperture is smaller than a size of the beam spot and the shade has athickness smaller than a wavelength of the laser beam.
 2. An opticalhead recited in claim 1, wherein the aperture is rectangular.
 3. Anoptical head recited in claim 1, wherein the transparent condensingmedium further includes a projection positioned in the aperture forrecording and/or reproducing by applying a near-field wave leaked fromthe projection, and the projection has a top surface where thenear-field wave leaks from, the top surface and a surface of the shadeform an almost flat surface.
 4. An optical head recited in claim 1,further comprising a base which fixes at least the transparentcondensing medium and the laser, wherein the base scans over a disk toread and/or write data.
 5. An optical head, comprising: a laser emittinga laser beam; a transparent condensing medium having a condense surfaceon which a condensed laser beam forms a beam spot; a shade provided onthe transparent condensing medium and having an aperture, wherein theaperture is positioned at which the beam spot is formed and an area ofthe aperture is smaller than a size of the beam spot; and apiezoelectric element which moves the transparent condensing medium. 6.An optical head, comprising: a laser emitting a laser beam; an opticalcondense element condensing the laser beam; a transparent condensingmedium having a condense surface on which a condensed laser beam forms abeam spot, wherein the transparent condensing medium is a SolidImmersion Lens or a Super Solid Immersion Lens; a shade provided on thetransparent condensing medium and having an aperture, wherein theaperture is positioned at which the beam spot is formed and an area ofthe aperture is smaller than a size of the beam spot; and a detectingsystem which detects a reflect beam from a recording medium making useof SCOOP method.
 7. An optical head, comprising: a laser emitting alaser beam; an optical condense element condensing the laser beam; atransparent condensing medium which has an incident surface on which thelaser beam is incident, a reflect surface which reflects the laser beambeing incident through the incident surface, and a condense surface onwhich the reflected laser beam condenses to form a beam spot; a shadeprovided on the transparent condensing medium and having an aperture,wherein the aperture is positioned at which the beam spot is formed andan area of the aperture is smaller than a size of the beam spot; and adetecting system which detects a reflect beam from a recording mediummaking use of SCOOP method.
 8. An optical head, comprising: a laseremitting a laser beam; an optical condense element condensing the laserbeam; a transparent condensing medium having a condense surface on whicha condensed laser beam forms a beam spot; a shade provided on thetransparent condensing medium and having an aperture, wherein theaperture is positioned at which the beam spot is formed and an area ofthe aperture is smaller than a size of the beam spot; a detecting systemwhich detects a reflect beam from a recording medium making use of SCOOPmethod; and a tracking system which executes a tracking of the recordingmedium by means of a sample servo system.
 9. An optical head,comprising: a laser emitting a laser beam; an optical condense elementcondensing the laser beam; a transparent condensing medium which has anincident surface on which the laser beam is incident, and a reflectsurface which reflects the laser beam being incident through theincident surface, and a condense surface on which the reflected laserbeam condenses to form a beam spot; a shade provided on the transparentcondensing medium and having an aperture, wherein the aperture ispositioned at which the beam spot is formed and an area of the apertureis smaller than a size of the beam spot; and a base which fixes at leastthe transparent condensing medium and the laser wherein the base scansover a disk to read and/or write data.